Such a circuit is disclosed in the British Patent Specification No. 1,556,235. One or more stabilised supply voltages are obtained with this known circuit. It appears that the voltage across the capacitor is higher than the input voltage, more specifically by a factor which depends on the ratio of the conduction period of the controllable switch to the period of the control signal thereof, so that the voltage across the capacitor can be kept substantially constant by controlling said ratio. The turning by means of the tuning capacitor limits the voltage across the switch during the period of time it is not conducting to a level which is not too high, and transients which might be produced by parasitic capacitances and which might cause undesirable radiation do not occur.
In practice the multiplying factor obtained with the prior art circuit cannot be of any arbitrary high value. This would imply that said ratio would come very close to 1, which might endanger the control properties of the circuit. In that event the recharging current of the capacitor would furthermore flow in a very short period of time and would consequently have a very high value, which might be too high for the circuit elements through which it flows.